<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>javascript</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box
    }
    body {
      font-size: 14px;
      padding: 20px;
    }
    ul li {
      line-height: 30px;
    }
  </style>
</head>
<body>
  <ul>
    <li></li>
  </ul>
</body>
<script>
  console.log('bSAD'.toLowerCase())
  console.log('adads'.toUpperCase())
  console.log(Math.floor('123.12'))
  console.log(Math.ceil(2.3))
  function isFloat(val) {
    return typeof val === 'number' && val.toString().indexOf('.') > -1
  }
  var sex =  Symbol('sex');
  var obj1 = {
    name: 'zhangli',
    age: '29',
    [Symbol('sex')]: 'nan'
  }
  var a = Symbol.for('name');
  var b = Symbol.for('name');
  console.log(Symbol.keyFor(a))

  var s = Object.getOwnPropertySymbols(obj1)[0]
  console.log(obj1[s])
  for(var key in obj1) {
    console.log(obj1[key]);
  }
  console.dir(obj1);
  var someVal = 1
  if(typeof someVal === 'undefined') {
    console.log(2);
  }
  let i = 0;
  while(++i < 10) {
    console.log(i)
  }
  let obj2 = {
    name: 'zhangli',
    sex: 'nan'
  }
  delete obj2['name'];
  console.log(obj2)
  let arr1 = [1,2,3,4];
  delete arr1[2];
  console.log(arr1[2]);
  var aa;
  console.log(typeof aa)
  var s = '1s';
  console.log(s++)
  console.log(!!'false')
  console.log(!!undefined)
  console.log(typeof -Infinity)
  console.log(false === '')
  console.log(typeof '2E+2')
  var bb = 3e+3
  console.log(bb++)
  var v = 100 || 10;
  console.log(v);
</script>
</html>